1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a storage device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a semiconductor device or a method for manufacturing a semiconductor device.
In this specification, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, an electro-optical device, a semiconductor circuit, and an electronic device may include a semiconductor device.
2. Description of the Related Art
A technique in which a transistor is formed using a semiconductor film has attracted attention. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor including an amorphous oxide semiconductor film containing indium (In), gallium (Ga), and zinc (Zn) is disclosed in Patent Document 1.
Techniques for improving carrier mobility by stacking oxide semiconductor films are disclosed in Patent Documents 2 and 3.
It is known that a transistor including an oxide semiconductor film has an extremely small leakage current (off-state current) when the transistor is off. For example, a low-power-consumption CPU utilizing such a small leakage current characteristic of a transistor including an oxide semiconductor film is disclosed (see Patent Document 4).